Kalmoduliin

Kalmoduliin, known in English as calmodulin, is a small, highly conserved calcium-binding messenger protein expressed in all eukaryotic cells. It comprises a single 149-amino-acid polypeptide containing four EF-hand motifs that bind Ca2+. In the absence of calcium, calmodulin exists in a closed conformation; binding of Ca2+ induces a conformational change that enables interaction with a broad set of target proteins. It functions as a universal intracellular calcium sensor and regulator of numerous cellular processes.

Calmodulin has no intrinsic catalytic activity. Its role is to transduce calcium signals by activating or modulating a diverse array of enzymes and proteins, including calcium/calmodulin-dependent protein kinases (CaMKs), calcineurin, myosin light-chain kinase (MLCK), nitric oxide synthase, and phosphodiesterases. The protein's interaction with targets is calcium-dependent and often provides precise temporal control of signaling events.

Genetically, humans express CALM1, CALM2, and CALM3, three closely related genes that produce highly similar 149-amino-acid calmodulin isoforms. Expression is widespread across tissues, ensuring a ubiquitous calcium-sensing mechanism.

Mutations in CALM genes have been linked to calmodulinopathies, including long QT syndrome and catecholaminergic polymorphic ventricular tachycardia, highlighting the importance of calmodulin in cardiac electrophysiology. In research contexts, calmodulin is used to study calcium signaling and as a component of calcium-sensitive biosensors.